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With the aim of assessing differentiation of greenhouse gas emissions as manipulated by plastic film mulching (PFM) from paddy field from a year-round perspective, we determined net ecosystem CO2 exchange (NEE, CO2 flux), CH4 and N2O fluxes from a rice–rapeseed rotation field. PFM and non-mulching (NM) treatments were set from 2014 to 2017 (May 2014 to April 2015, May 2015 to April 2016 and May 2016 to April 2017 were set as Annual 1, Annual 2 and Annual 3, respectively) in Southwest China. Compared with NM, CH4 emissions were increased by 60.00% (P

The lack of carbon sources severely inhibits denitrification in wastewater with a low C/N ratio. Corncob and rice straw were chosen as supplementary carbon sources to bring into the wetland system to supplement the carbon sources needed for denitrification, and the enhancing effects of the two carbon sources on nitrogen removal from the wetland were studied. The cumulative release of carbon was in the order of rice straw[(145.17±9.44) mg·g

With the purpose of fully understanding the potential toxicity of heavy metals of various particle sizes in fly ash (FA) and finding an optimal chemical reagent stabilization scheme for fly ash with single or mixture reagents, basic physicochemical characteristics of FA was investigated using multiple chemical stabilization reagent schemes to stabilize heavy metals. The following compounds were used to develop single and mixed chemical stabilization schemes for heavy metals in waste incineration FA: sodium sulfide (Na2S), sodium dihydrogen phosphate (NaH2PO4), ammonium dibutyl dithiophosphate (DDTP), and 2,4,6-tri-mercapto-S-triazine trisodium salt (TMT-15). The results showed that the various particle sizes of FA were mainly distributed in the range of 48–1700 μm. FA was packed with heavy metals, and the smaller the particle size, the more toxic it was. The speciation distribution of Cu, Zn, Pb, Cd, and Cr in different particle sizes was identical to that of the mixed samples. In the experiments of single reagent stabilization scheme, 8% Na2S, 8% NaH2PO4, 4.2% DDTP or 4.2% TMT-15 could decrease the leaching concentration to meet the limits set by Chinese law, but 8% Na2S adding scheme had the lowest cost among them. However, in the mixture reagent scheme, 1.2% Na2S, 1.2% NaH2PO4 and 0.8% DDTP was more effective and even cheaper than other mixture or single schemes.

The aim of this research was to examine the effects of biochar addition (B0:0 t·hm

The type and structure of the substrate in constructed wetland affects the diversity and abundance of microorganisms, thereby influencing the effect of sewage treatment. In this study, four groups of wetlands were constructed in the greenhouse:blank-constructed wetland (CW0), hematite-constructed wetland (CW1), biochar-constructed wetland (CW2), and hematite+biochar-constructed wetland (CW3), to study the differences in sewage treatment effects, greenhouse gas emissions, and microbial community structures of constructed wetland systems under different filler substrates. The results showed that the addition of hematite or biochar increased the COD removal rate of -0.12% to 1.7%. The addition of biochar increased the removal rate of NH

As the problem of global warming becomes increasingly serious, the greenhouse gas (GHG) emission reduction measures of constructed wetlands (CWs) have drawn significant attention. Ferric-carbon micro-electrolysis exhibits an excellent effect on wastewater purification as well as the potential to reduce GHG emissions. Therefore, to explore the impact of ferric-carbon micro-electrolysis on GHG emissions from intermittent aeration constructed wetlands, four kinds of different wetlands with different fillers were constructed. The four fillers were ferric-carbon micro-electrolysis filler+gravel (CW-Ⅰ), ferric-carbon micro-electrolysis filler+zeolite (CW-Ⅱ), zeolite (CW-Ⅲ), and gravel (CW-Ⅳ). Intermittent aeration technology was used to aerate the wetland systems. The results show that ferric-carbon micro-electrolysis significantly improved the nitrogen removal efficiency of the intermittent aeration constructed wetlands and reduced GHG emissions. Compared with CW-Ⅳ, the CH

Ferric-carbon micro-electrolysis fillers and zeolite have been increasingly used as substrates in constructed wetlands due to their good wastewater pollution-removal efficiencies. To explore the effects of different fillers on wastewater treatment in constructed wetlands, four constructed wetlands were examined with vertical subsurface flow areas filled with ferric-carbon micro-electrolysis filler+gravel (CW-A), ferric-carbon micro-electrolysis filler+zeolite (CW-B), zeolite (CW-C), and gravel (CW-D). In addition, intermittent aeration was used to improve the dissolved oxygen (DO) environment. The results showed that, compared with CW-D, the ferric-carbon micro-electrolysis filler significantly increased the dissolved oxygen (DO

Investigate the effects of plastic film mulching on CH

To understand the atmospheric quality of the Beibei District of Chongqing, using the simultaneous observation data of aerosol optical depth and particulate matter concentration in 2014, we analyzed the characteristics of aerosol optical depth (AOD) in the urban area of Beibei and its correlation with particle concentration. The results showed that the annual average of AOD

A field experiment was conducted at the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China at the farm of Southwest University in Chongqing. In the study, static chamber and gas chromatography methods were used to study the effects of plastic film mulching treatment on CO

To investigate the effects of plastic film mulching and nitrogen fertilizer application on CH

Permanently flooded rice fields, a special kind of all year-round flooded rice fields in China, where the crop system is summer rice ( Oryza sativa ‘Q You 6′) with winter fallow, contribute to both CH 4 and N 2 O emissions. To investigate their CH 4 and N 2 O emissions over a whole year (November 2009 to October 2010) and responses to long-term tillage-cropping systems, four treatments after the conversion of such rice fields were examined: conventional tillage with a single summer rice and floodwater winter fallow (CTRF) or drained winter rapeseed ( Brassica napus ‘W You 25′) (CTRR), no-tillage narrow- or wide-ridge with a rice and rapeseed rotation (NTNRR or NTWRR). Results showed that CTRF emitted the highest CH 4 owing to permanently flooding water layer and higher soil organic carbon concentrations. Compared to CTRF, CH 4 emissions under other three tillage-cropping systems were decreased not only in the winter season but also in the rice-growing season. In contrast, N 2 O emissions over a whole one-year rice-rapeseed rotation cycle were almost equivalent to each other under these four tillage-cropping systems. Also compared to CTRR, the two no-tillage-cropping systems tended to enhance CH 4 while decrease N 2 O emissions, though with insignificant effects. The annual cumulative emissions of CH 4 and N 2 O were highest under CTRF (1.07 ± 0.20 kg CO 2 -eq ha −1 kg −1 yield) and significantly decreased under CTRR, NTNRR and NTWRR (0.59 ± 0.10, 0.67 ± 0.05 and 0.58 ± 0.09 kg CO 2 -eq ha −1 kg −1 yield, respectively), indicating that the summer rice-winter rapeseed rotation system, irrespective of tillage management, rather than the summer rice-winter fallow system, had achieved the objective of higher yields with less greenhouse gas emissions. These results demonstrate that the no-tillage wide-ridge with a rice and rapeseed rotation (NTWRR) is the most efficient management in terms of decreasing CH 4 and N 2 O emissions in Southwest China.

To investigate the effects of plastic film mulching and nitrogen fertilizer application on N

A field experiment was conducted at the Key Field Station for Monitoring Eco-environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University, Chongqing. The static chamber and gas chromatography method was used to study the effect of the cropping systems on greenhouse gases from rice-fallow (RF), rice-rapeseed rotation (RR), and rice-brussel mustard rotation (RV) cropland

In order to study the concentration and distribution characteristics of water-soluble inorganic ions in aerosol particles of the Beibei district of Chongqing, aerosol samples were collected with an Andersen cascade impactor between March 2014 and February 2015. Water-soluble inorganic ions, including Na

To study the pollution characteristics of atmospheric carbon aerosols, aerosol samples were collected via a cascade impactor (Andersen) from March 2014 to February 2015 in Beibei District, Chongqing. Organic carbon (OC) and element carbon (EC) were detected using a DRI 2001A carbon analyzer. The results showed that the annual average concentrations of OC and EC in PM

A field experiment was conducted in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University in Chongqing. Static opaque chamber and gas chromatography methods were used to study the effect of plastic film mulching on CH

In order to understand the changes of dissolved carbon and dissolved nitrogen in the water of Three Gorges Reservoir,this research was carried out once a week by the bank of Yangtze River in Fuling beach from March 2011 to August 2012,and the variation characteristics of dissolved C,N composition and their source were analyzed.The results showed that the concentration of DOC ranged from 0.64 mg·L

Considering the common cropping system (chili-radish rotation) in Southwest China, the objective of this study is to explore the effect of plastic film mulching on N

Taking a typical drawdown area located in Wangjiagou of the Three Gorges Reservoir as the study object, four elevations 180,175,165 and 155 m were selected to explore the effect of water level change on soil microbial biomass carbon (SMBC) and microbial biomass nitrogen (SMBN). Wherein, 175,165 and 155 m elevations located in the fluctuating zone, manifested as short, medium and long-term flooding, respectively; 180 m was used as the control, located on the land and never flooded. Sampling depth in soil samples was 0-20 cm, collected once a week. The results indicated that, soil organic carbon (SOC) and total nitrogen (TN) contents at 180 m had no obvious seasonal changes, while they showed remarkable seasonal trends at 175m, which in spring and summer were significantly higher than in autumn and winter; SMBC and SMBN contents and their allocation ratio at four elevations were similar and had significant seasonal fluctuation, which were highest in autumn and lowest in summer at each elevation, indicating that in drawdown area the microbial activity and turnover rate of soil organic carbon and nitrogen were limited by the high-temperature and low-humidity soil environment in summer. Data analysis showed that, compared with the 180 m elevation, contents of SOC, TN, SMBC and microbial quotient, SMBN and its allocation proportion showed varying degrees of increase, while contents of these indexes were significantly lower than control except SMBN and its allocation proportion, meaning that compared with 180 m short and medium-term flooding was conducive to improve soil carbon, nitrogen and their turnover rate and microbial biomass, however, contents of soil carbon and nitrogen and microbial biomass carbon were significantly restricted at 155 m as soil was subjected to flooding stress, meanwhile the turnover rate of SOC was reduced. Correlation analysis implied that SMBC and SMBN had very significant negative correlation with temperature at 5 cm soil depth and pH, meaning that the two environmental factors had a strong effect on soil microbial biomass.

Five levels (180 m, 175 m, 165 m, 155 m, and 140 m) in a typical drawdown area in Wangjiagou in the Three Gorges Reservoir were selected to study CH

Three heights (180 m, 175 m and 155 m) located in a typical drawdown area in Wangjiagou of the Three Gorges Reservoir were selected for studying the N

Using the static opaque chamber method and choosing a chili-radish cropping system, a field experiment, located in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University in Chongqing, was conducted

A total of 87 daily PM

In this study, four land use types including subtropical evergreen broad-leaved forest (abbreviation: forest), sloping farmland, orchard and abandoned land were selected to collect soil samples from 0 to 60 cm depth at the same altitude in Jinyun Mountain. Four sizes of large macroaggregates (2 mm), small macroaggregates (0.25-2 mm), microaggregates (0.053-0.25 mm) and silt + clay (0.053 mm) were achieved by wet sieving method and the contents of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in each aggregate fraction were measured to study the impacts of the different land use types on MBC and MBN in soil aggregates. The results showed that the contents of MBC and MBN in all aggregates in the four land use types decreased with the increasing soil depth. Except large macroaggregetes, the contents of MBC and MBN in the other three soil aggregates decreased when the forest was reclamated into orchard and sloping farmland. MBC and MBN contents in large macroaggregates, small macroaggregates and microaggregates all increased when the sloping farmland was abandoned. The storages of organic carbon and nitrogen in soil depth of 0-60 cm in the four proportions were calculated by the equivalent soil mass method. The results revealed that MBC storages in the other three sizes except silt + clay were higher in the forest than those in orchard and sloping land. And MBC storages in the all aggregates were higher in the abandoned land than those in the sloping land. MBN storages in small macroaggregates and microaggregates were higher in the forest than those in orchard and sloping land. And MBN storages in the other three aggregates except silt + clay were higher in the abandoned land than those in the sloping land. Generally speaking, the storages of MBC in soil aggregates of forest and abandoned land were higher than in orchard and sloping land, MBN storage in soil aggregates of forest was nearly equal to the storage in orchard. However, the storages of MBN in soil aggregates of forest and abandoned land were higher than those in sloping land. The results showed that the reclamation of the forest resulted in the loss of MBC and MBN in soil aggregates of sloping land. However, the abandon of the sloping land contributed to the acumulation of MBC and MBN in soil aggregates. In the process of land use change, the direction and quantity of change in MBC in the soil aggregates were not consistent with those of the total soil organic carbon, which meant the microbial quotient in soil aggregates was not suitable for using to evaluate the impact of land use change on soil quality, using the total organic carbon as an index to express the sensitivity of the land use change may be better.

In this paper, we take Jinyun Mountain where located in Beibei district of Chongqing as the research object and explore the effect of different ways of land use on soil active organic carbon, nitrogen components by collecting the soil samples from 0 to 60 cm depth in subtropical evergreen broad-leaved forest (hereinafter referred to as the forest), abandoned land, orchard, farmland and measuring the content of MBC, MBN, DOC and DON. The research results show that the contents of soil MBC, MBN, DOC, DON are reduced with the increase of soil depth in four types of land using soils. Variance analysis of the single factor shows that four kinds of land uses have no significant difference in the contents of MBC, MBN and DON, but the DOC content of the abandoned land is significantly higher than that of other three kinds. It shows that the different ways of land use have no obvious effects on soil MBC, MBN and DON but the abandonment of slope cropland can significantly increase the content of soil DOC. There is no significant difference among the distribution ratio of MBN, DOC, DON in forest, abandoned land, orchard and farmland within the soil from 0 to 60 cm, but the distribution ratio of slope MBC is significantly higher than that of other three kinds. It means farmland soil organic carbon has a higher biological activity, this could due to the application of green manure, farmland manure and other organic fertilizers. Under different land utilizations, DOC/DON is the highest, MBC/MBN is the second, and SOC/TN is the lowest. It means the biological solidification of dissolved organic matter is the strongest, and the mineralization of soil organic matter is the most obvious. Under the four kinds of land uses, there are the lowest ratios in SOC/TN, MBC/MBN and DOC/DON in the farmland. And all the ratios are less than 20, which suggest that the mineralization of farmland soil organic matter is stronger and it's easy to cause the loss of soil carbon.

The manganese contents of soils and dominant plants from the manganese mining areas in Xiushan autonomous county of Chongqing were researched in this paper. The results showed that the Mn pollution of soil in the Mn mining tailings were very serious with high indexes (Igeo>5), and sewage irrigated soil was also contaminated by manganese metal. The uptake of Mn by dominant plants can be classified into three types according to the Mn contents in plant shoots and roots, (1) the accumulator which absorbs a large content of Mn by the roots and transports it to the shoots, (2) the root compartment which also absorbs a large content of Mn but mainly in the roots, and (3) the excluder which absorbs a smaller content of Mn than the accumulator. The edible parts of radishes and peppers growing in the Mn mining tailings and cropland were all seriously polluted by manganese and not safe for human health.

The distributions in different particle sizes of municipal solid waste incinerator (MSWI) fly ash in spring and autumn were studied by sieve method, and the heavy metal contents of Cu, Zn, Mn, Pb, Cd, Ni, Cr and Hg in different size particles were measured, and the heavy metal leaching amount in the different particle size were also studied under the GB5085.3-2007 and USEPA-TCLP leaching procedure, respectively. The results showed that the particle size of fly ash in autumn was relatively smaller than that of in spring, more than 90% of particle size of fly ash in spring and autumn were less than 250 μm, and the particle size in 83-105 μm of fly ash in spring distributes in most with about 40% of the total, but 105-149 μm in autumn distributes in most, accounted for about 45% of the total. The content of heavy metals decreased first and then increased with the decreasing particle sizes except for Ni, and the content of heavy metals in the spring is higher than that of in autumn except for Fe and Zn. Under the GB5085.3-2007 leaching procedure, the leaching content of Cu, Zn and Ni in MSWI fly ash in both spring and autumn and Cr in spring were not beyond limited standard, but Pb and Cd in both spring and autumn and Cr in autumn were beyond limited standard. However, under TCLP leaching procedure, the leaching content of Pb, Cr and Cd in both spring and autumn were beyond the standard limits.

Two thiol collectors, sodium diethyldithiocarbamate (DDTC) and potassium ethyl xanthate (EXT), were adopted to stabilize hexavalent chromium from chromic slag. The average usage of each thiol collector is 62.5 μmol∙g-1 in chromic slag. The leaching characteristic of Cr6+ in chromic slag was analyzed according to the acidic extraction process with the toxicity characteristic leaching procedure (TCLP) and the procedures of extraction in water with the horizontal vibration method (HMV). Under the 0.1 mol∙L-1 TCLP and HMV conditions, we compared them with FeSO4 and found that two thiol collectors presented better stabilization effects for Chromium (VI) from chromic slag, especially the effect by DDTC is more stabilized than that by EXT. The rate of their stabilized treatments is 78.42% and 83.18%, respectively, which both are obviously higher than that by FeSO4. Heavy metal-thiol collectors such as flocculent mass is more stabilized under the neutral and alkalized conditions (pH>8), but it may be partly dissolved under the acidic conditions (pH6+ from chromic slag will increase quickly with pH decreasing.

The impact of conservation tillage practices on carbon sequestration has been of great interest in recent years. This experiment analyzed the organic carbon status of soils sampled at depth increments from 0 to 60 cm after 20 years in a purple paddy soil. The tillage experiment was established in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China, located in the farm of Southwest University (30°26′N, 106°26′E), Chongqing. In this paper, five tillage treatments including conventional tillage with rice only system (DP), conventional tillage with rotation of rice and rape system (SL), no-till and ridge culture with rotation of rice and rape system (LM), no-till and plain culture with rotation of rice and rape system (XM) and tillage and ridge culture with rotation of rice and rape system (LF) were selected as research objectives to measure SOC storage and stratification ratio of SOC (CSR). The SOC storage under different tillage systems was calculated based on an equivalent soil mass. The CSR can be used as an indicator of soil quality because surface organic matter is essential to erosion control, water infiltration, and the conservation of nutrients. Results showed that in soil under no-till SOC was concentrated near the surface, while in tilled soil SOC decreased equably with the increase of soil depth. The difference of SOC contents between the five tillage systems was the largest in the top soil and the lowest in the bottom soil. The order of SOC storage was LM (158.52 Mg C•ha-1) >DP (106.74 Mg C•ha-1) >XM (100.11 Mg C•ha-1) >LF (93.11 Mg C•ha-1) >SL (88.59 Mg C•ha-1), LM treatment was significantly higher than the other treatments. The CSR of 0-10/50-60 cm was 2.65, 2.70 and 2.14 under LM, XM and LF treatments, while 1.54 and 1.92 under DP and SL treatments. We considered CSR>2 indicate an improvement in soil quality produced by changing from tillage to no-tillage, as well as changing from plane to ridge. Overall, long-term LM treatment is a valid strategy for increasing SOC storage and improving soil quality in a purple paddy soil in Southwest China.

The effect of different tillage systems on the soil organic carbon (SOC), active organic carbon (AOC) and remaining organic carbon (ROC) were studied in a long-term experiment in Chongqing, China. The experiment included five tillage treatments, which are conventional tillage with rice only system (DP), conventional tillage with rotation of rice and rape system (SH), no-till and ridge culture with rotation of rice and rape system (LM), no-till and plain culture with rotation of rice and rape system (XM) and tillage and ridge culture with rotation of rice and rape system (LF), respectively. The results showed that the content of SOC declined as the soil depth increased, and presented obvious surface enrichment phenomenon under the no-tillage systems. The order of SOC, AOC, ROC and ROC/SOC in the 0–60 cm soil layer under different tillage systems was LM (22.74 g kg-1) > DP (14.57 g kg-1) > XM (13.73 g kg-1) > LF (13.10 g kg-1) > SH (11.92 g kg-1), DP (3.67 g kg-1) > LF (3.49 g kg-1) > LM (3.28 g kg-1) > XM (3.17 g kg-1) > SH (2.69 g kg-1), LM (18.09 g kg-1) > DP (10.34 g kg-1) > XM (10.12 g kg-1) > LF (9.20 g kg-1) > SH (8.80 g kg-1) and LM (85%) > SH (78%) > XM 77%) > LF (75%) > DP (74%). Compared with other systems, LM significantly increased SOC, ROC and ROC/SOC, which indicated long-term LM system performed good effect for carbon sequestration.

The effect of different tillage systems on the size distribution of aggregates and organic carbon distribution and storage in different size aggregates in a Hydragric Anthrosol were studied in a long-term experiment in Chongqing, China. The experiment included five tillage treatments, which are conventional tillage with rice only system (DP), conventional tillage with rotation of rice and rape system (SH), no-till and ridge culture with rotation of rice and rape system (LM), no-till and plain culture with rotation of rice and rape system (XM) and tillage and ridge culture with rotation of rice and rape system (LF), respectively. The results showed that the aggregates 0.25-0.05 mm in diameter accounted for the largest proportion in each soil layer under all treatments. The organic carbon mainly exist in aggregates in the 0.25-2 mm and 0.05-0.25 mm diameter in the plough layer, which mainly exist in the 0.25-2 mm in diameter in the bottom layer. Distribution of organic carbon in aggregates in the 0.05-0.25 mm diameter class was highest, followed by the aggregates in the 0.25-2mm diameter class. The organic carbon in aggregates under different tillage systems was in a decreasing order of LM (21.05 g·kg-1)> DP (14.13 g·kg-1)> XM (13.29 g·kg-1)> LF (12.54 g·kg-1) > SH (11.41 g·kg-1). The total organic carbon content showed a significant correlation with the amount of aggregates with diameter >0.005 mm. The results showed that the accumulation of soil organic carbon was mainly affected by aggregates in the >0.005mm diameter class.

Four land utilization patterns were selected for this study in Jinyun mountain, including subtropical evergreen broad-leaved forest (abbreviation: forest), sloping farmland, orchard and abandoned land. Soil samples were taken every 10 cm in the depth of 60 cm soil and proportions of large macroaggregates (2 mm), small macroaggregates (0. 25-2 mm), microaggregates (0. 053 - 0. 25 mm) and silt + clay (0. 053 mm) were obtained by wet sieving method to measure the content of organic carbon and labile organic carbon in each aggregate fraction and analyze impacts of land uses on organic carbon and labile organic carbon of soil aggregates. LOC content of four soil aggregates were significantly reduced with the increase of soil depth; in layers of 0-60 cm soil depth, our results showed that LOC contents of forest and abandoned land were higher than orchard and sloping farmland. Reserves of labile organic carbon were estimated by the same soil quality, it revealed that forest (3. 68 Mg.hm-2)abandoned land (1. 73 Mg.hm-2)orchard (1. 43 Mg.hm-2)sloping farmland (0.54 Mg.hm-2) in large macroaggregates, abandoned land (7.77, 5. 01 Mg.hm-2)forest (4. 96, 2.71 Mg.hm-2)orchard (3. 33, 21. 10 Mg.hm-2)sloping farmland (1. 68, 1. 35 Mg.hm-2) in small macroaggregates and microaggregates, and abandoned land(4. 32 Mg.hm-2)orchard(4. 00 Mg.hm-2)forest(3. 22 Mg.hm-2)sloping farmland (2.37 Mg.hm-2) in silt + clay, forest and abandoned land were higher than orchard and sloping farmland in other three soil aggregates except silt + clay. It was observed that the level of organic carbon and labile organic carbon were decreased when bringing forest under cultivation to orchard or farmland, and augments on organic carbon and labile organic carbon were found after exchanging farmland to abandoned land. The most reverses of forest and abandoned land emerged in small macroaggregates, orchard and sloping farmland were in microaggregates. That was, during the transformations of land utilization pattern, soil aggregates with bigger size were easier to accumulate or lose labile organic carbon. Allocation ratios of labile organic carbon to soil organic carbon under four land uses were decreased as the soil depth added. Allocation ratios of orchard and sloping farmland were a bit higher than forest and abandoned land, which indicated that organic carbon of forest and abandoned land were more steady and available for soil as a carbon sink, meanwhile, the forest and abandoned land would avoid more CO2 diffusing to the atmosphere from the decomposition of soil organic carbon.

Four land types including the subtropical evergreen broad-leaved forest, sloping farmland, orchard and abandoned land were selected to collect soil samples from 0 to 60 cm depth at the same altitude of sunny slope in the Jinyun Mountain in this study. Soil light fraction organic carbon and nitrogen ( LFOC and LFON), and particulate organic carbon and nitrogen (POC and PON) were determined and the distribution ratios and C/N ratios were calculated. The results showed that the contents of LFOC and LFON decreased significantly by 71. 42% and 38. 46% after the forest was changed into sloping farmland (P0. 05) but the change was not significant when it was changed into orchard (P0. 05), while the contents of LFOC and LFON increased significantly by 3. 77 and 1. 38 times after the sloping farmland was changed into abandoned land (P0. 05). The contents of POC and PON did not vary markedly after the forest was converted into orchard or sloping farmland, while the POC and PON contents increased markedly by 4. 12 and 1. 25 times after the sloping farmland was abandoned. Those above results indicated that abandoned land was easy for active organic carbon and nitrogen accumulation; on the contrary, sloping farmland was easy to lose soil labile carbon and nitrogen. The LFOC and LFON distribution ratios were significantly reduced by 31. 20% and 30. 08%, respectively after the forest was changed into the sloping farmland, and increased by 18. 74% and 20. 33% respectively after the forest was changed into the orchard. Nevertheless, the distribution ratios of LFOC and LFON were changed little by converting the forest into the sloping farmland and orchard. The distribution ratios of LFOC, LFON, POC and PON all increased significantly after the farmland was abandoned (P0. 05). Those results showed that the activity of soil organic carbon and nitrogen was enhanced after forest reclamation, while reduced after the sloping farmland was abandoned. The ratios of carbon to nitrogen in soil organic matter, light fraction organic matter and particulate organic matter were in the order of abandoned land (12. 93)forest (8. 53)orchard (7. 52)sloping farmland (4. 40), abandoned land (16. 32)forest (14. 29)orchard (11. 32)sloping farmland (7. 60), abandoned land (23. 41)sloping farmland (13. 85 )forest (10. 30)orchard (9. 64), which indicated that the degree of organic nitrogen mineralization was higher after forest cultivation and lower after the sloping farmland was abandoned.

Soil aggregates have the important effect on soil fertility, soil quality and the sustainable utilization of soil, and they are the mass bases of water and fertilizer retention ability of soil and the supply or release of soil nutrients. In this paper, in order to study the impact of land use type on stability and organic carbon of soil aggregates in Jinyun Mountain, we separated four land use types of soil, which are woodland, abandoned land, orchard and sloping farmland by wet sieving method, then we got the proportion of large macroaggregates (2 mm), small macroaggregates (0.25-2 mm), microaggregates (53 μm-0.25 mm) and silt + clay (53 μm) and measured the content of organic carbon in each aggregate fraction in soil depth of 0-60 cm and calculated the total content of organic carbon of all aggregates fraction in each soil. The results showed that reclamation of woodland will lead to fragmentation of macroaggregates and deterioration of soil structure, and the proportion of macroaggrgates (0.25 mm) were 44.62% and 32.28% respectively in the soils of orchard and sloping farmland, which reduced 38.58% (P0.05) and 91.52% (P0.05) compared with woodland. While after changing the sloping farmland to abandoned land, which lead to the conversion of soil fraction from silt + clay to large macroaggregates and small macroaggregates, so it will improve the soil structure. MWD (mean weight diameter) and GMD (geometric mean diameter) are important indicators of evaluating the stability of soil aggregates. We found the MWD and GWD in soil depth of 0-60 cm in orchards and sloping farmland were significantly lower than those in woodland (P0.05), while after changing the sloping farmland to abandoned land, the MWD and GWD increased significantly (P0.05), which indicated that reclamation of woodland will lead to the decrease of stability of soil aggregates, and they will be separated more easily by water. However, after changing the sloping farmland to abandoned land will enhance the stability of soil aggregates, and improve the ability of soil to resist external damage. The organic carbon content in each soil aggregate of four land use types decreased with the increase of soil depth. In soil depth of 0-60 cm, the storage of organic carbon of large macroaggregates in each soil are in orders of woodland (14.98 Mg x hm(-2))abandoned land (8.71 Mg x hm(-2))orchard (5.82 Mg x hm(-2))sloping farmland (2.13 Mg x hm(-2)), and abandoned land (35.61 Mg x hm(-2))woodland (20.38 Mg x hm-(-2))orchard (13.83 Mg x hm(-2))sloping farmland (6.77 Mg x hm(-2)) in small macroaggregates, and abandoned land (22.44 Mg x hm(-2))woodland (10.20 Mg x hm(-2))orchard (6.80 Mg x hm(-2))sloping farmland (5. 60 Mg x hm(-2)) in microaggregates, and abandoned land (22.21 Mg x hm(-2))woodland (17.01 Mg x hm(-2))orchard (16.70 Mg x hm(-2))sloping farmland (9.85 Mg x hm(-2)) in silt and clay fraction. Storage of organic carbon in each aggregate in the soils of woodland and abandoned land were higher than those in the soils of orchard and sloping farmland, which indicated that reclamation of woodland will lead to a loss of organic carbon in each soil aggregate fraction, while after changing the sloping farmland to abandoned land will contribute to restore and sequestrate the soil organic carbon. In addition, it showed that most organic carbon accumulated in small macroaggregate in soils of woodland and abandoned land, while they are in silt and clay in soils of orchard and sloping farmland, indicating that organic carbon in larger aggregates is unstable and is easier to convert during the land use change.

In order to study the composition and distribution of VOCs (Volatile Organic Compounds) in the atmosphere in the urban area of Beibei district, Chongqing, atmospheric samples were collected from March 2012 to February 2013 with special stainless steel cylinders, and analyzed with a three-stage preconcentration method coupled with GC-MS. 78 species of VOCs were detected in this study, of which there were 25 species of alkanes, 15 species of olefins, 28 species of aromatic hydrocarbons and 10 species of halogenated hydrocarbons. The results showed that the top seven species of VOCs according to the order of annual average concentration in the atmosphere of Beibei were: Dichloromethane (3. 08 x 10(-9) ) , Benzene (2. 09 x 10-9) , Isopentane (1. 85 x 10 -9) , Toluene (1. 51 x 10(-9)) , Propane (1. 51 x 10(-9)), m/p-xylene (1.43 x 10(-9)) and Styrene (1. 39 x 10-9). The concentration of TVOCs (Total Volatile Organic Compounds) in the atmosphere of Beibei was 33. 89 x 10 -9 during the measuring period, and the seasonal variation was obvious with the order of spring (42. 57 x 10 -9)autumn (33.89 x 10-9)winter (31.91 x 10 -9)summer (27.04 x 10(-9)). In the composition of TVOCs, alkanes and aromatic hydrocarbons provided the largest contribution to TVOCs (31.5% and 30.7% ) , followed by halogenated hydrocarbon, accounting for 27.4% , and the last one was olefins, with only 10.4%. By means of ozone formation potential, the analysis results showed that olefins and aromatic hydrocarbon compounds were the two important materials which made the biggest contribution to the formation of ozone in the atmosphere of Beibei. We further analyzed the sources of VOCs in atmosphere of Beibei by the method of Principal Component Analysis (PCA). Vehicle exhaust was the biggest source and its contribution to VOCs was 50. 41%. The calculated results with T/B value also confirmed that traffic was the biggest source contributing to the VOCs in atmosphere of Beibei.

To study the characteristics of atmospheric pollutants in the urban area of Beibei district of Chongqing, the concentrations of the atmospheric pollutants were measured by automatic on-line continuous monitoring equipments from Jan. 2012 to Feb. 2013. The results showed that the concentrations of the pollutants often exceeded the corresponding values of the new National Ambient Air Quality Standards (GB 3095-2012) except SO2. Of these pollutants, PM2.5 was the most serious in this area. The concentrations of the atmospheric pollutants had significant seasonal variation. The concentrations of O3 and O(x) were both the highest in summer and the lowest in winter. The average concentrations of O3 were (36.1 +/- 19.2), (48.8 +/- 32.6), (29.8 +/- 28.6) and (18.2 +/- 15.8) microg x m(-3), and the average O(x) concentrations were (77.6 +/- 20.6), (91.3 +/- 37.6), (77.5 +/- 30.6) and (69.4 +/- 18.2) microg x m(-3) in spring, summer, autumn and winter in 2012, respectively. The concentrations of NO(x) appeared higher in winter and lower in summer, the average concentrations of NO, NO2 and NO(x) were (11.8 +/- 9.4), (42.3 +/- 13.1) and (54.1 +/- 20.8) microg x m(-3) in spring, (8.2 +/- 4.9), (40.5 +/- 9.9) and (48.7 +/- 12.6) microg x m(-3) in summer, (20.7 +/-17.1), (47.2 +/- 14.1) and (67.9 +/- 25.5) microg x m(-3) in autumn, and (30.4 +/- 25.1), (51.2 +/- 15.9), (81.6 +/- 37.9) microg x m(-3) in winter. The concentrations of SO2 appeared higher in spring and winter, and lower in summer and autumn. The concentrations of SO2 were (50.5 +/- 23.3), (26.3 +/- 16.7), (38.8 +/- 18.4) and (53.7 +/- 23.4) microg x m(-3) in spring, summer, autumn and winter, respectively. The concentrations of PM2.5 appeared higher in winter and changed smoothly in other seasons, with the average concentration of (61.4 +/- 28.5), (68.1 +/- 32.5), (61.9 +/- 27.1) and (89.6 +/- 44.2) microg x m(-3) in spring, summer, autumn and winter, respectively. The curves of diurnal variations of O3, O(x), NO, NO(x) and SO2 all showed single peak. However, the time of the peak values varied for different pollutants, 16:00 for O3 and O(x), and 8:00-11:00 for NO, NO(x) and SO2. The diurnal variations of NO2 and PM2.5 were similar to the two peaks that appeared in the morning and at night, respectively. Moreover, the diurnal ranges of O3 and O(x) concentrations were much wider in summer, while the wider ranges were observed in winter for NO, NO2, NO(x), SO2 and PM2.5. There was no difference in the diurnal pattern of NO between weekends and weekdays, the concentrations of N2O in weekdays were much higher than those on weekends, but with O3 the situation was the opposite. Correlation analysis indicated that the O3 concentration was positively correlated with temperature and wind speed, while negatively correlated with relative humidity. However, the situation of NO(x) was the opposite. PM2.5 concentration was negatively correlated with temperature and wind speed, while positively correlated with relative humidity. SO2 concentration had different correlations with the meteorological parameters in different seasons. In addition, wind direction was an important factor affecting the concentrations of the atmospheric pollutants.

The impacts of different land use on soil organic matter (SOM), soil labile organic matter (SLOM) and their efficiency ratios (ER), and soil carbon management index (CMI) were studied in this study. Subtropical evergreen broad-leaved forest (abbreviation: forest) , sloping farmland, orchard and abandoned land were selected and soils at the depths of 0-10, 10-20, 20-30, 30-40, 40-50 and 50-60 cm were sampled in the spring of 2011 to determine the contents of soil organic matter and labile organic matter. The results showed that the contents of soil organic matter and soil labile organic matter both decreased with the increase of soil depth under all four land use types; however, forest and orchard enriched SOM and SLOM contents in the 0-10 cm and 0-20 cm soil layers, respectively, while the contents of SOM and SLOM decreased evenly in sloping farmland and abandoned land. In the whole soil layer (0-60 cm) , the order of SOM and SLOM contents was abandoned landforestorchardsloping farmland, indicating that at the conversion from forest into orchard or sloping farmland, SOM was reduced by 21.56% (P0.05) and 55.90% (P0.05), respectively, and at the conversion from sloping farmland into abandoned land, the low SLOM, middle SLOM and high SLOM increased by 144.2% (P0.05) , 153.3% (P0.05) and 242.7% (P0.05), respectively. There was no significant difference in low ER, middle ER and high ER among the four land uses as suggested by ANOVA which showed that SRs were not sensible to the change of land use. All three CMis were in the order of abandoned landforestorchardsloping farmland, revealing that forest reclamation resulted in the reduction of soil organic carbon storage and the decline of soil quality, and the abandonment of sloping farmland would increase soil carbon sink and improve soil quality. Three kinds of SLOM were all positively correlated with soil total nitrogen, available phosphorus and available potassium, while negatively correlated with soil density bulk, indicating that SLOM had close relationships with soil physical and chemical characters and could be used as an important index to reflect soil nutrient status and judge soil quality.

The seasonal dynamics of soil organic carbon (SOC), readily oxidized carbon (ROC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC) in a purple paddy soil were studied in a long-term field experimental station in Chongqing, China. The results showed that the seasonal variations of the contents of SOC, ROC and MBC had similar trends in the rape growing season. The contents were much higher in the early and late stages than in the middle stage of the rape growth. SOC, ROC and MBC all achieved the highest values of 16.20 g x kg(-1), 3.58 g x kg(-1) and 309.70 mg x kg(-1) at the end of the growing period, respectively. The seasonal change of DOC content presented as a single peak and reached to the highest value of 37.64 mg x kg(-1) at the middle stage of the rape growth. The temporal dynamics of the allocation ratios of ROC, MBC and DOC were similar to that of their contents. The allocation ratios of ROC, MBC and DOC were 15.49%-23.93%, 1.44%-2.06% and 0.11%-0.32% during the rape growing season, respectively. The influencing factors of SOC and ROC contents were the soil temperature at 5 cm soil depth, soil total nitrogen content and pH. MBC content was jointly impacted by the soil temperature at 5 cm soil depth, root biomass and its C and N contents. DOC content was mainly affected by soil moisture.

Using the static opaque chamber method, a field experiment, located in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University (30 degrees 26'N, 106 degrees 26'E) in Chongqing, was conducted in situ for one year to study the effect of different tillage systems on CH4 and N2O emission from ago-ecosystems in a purple paddy soil. In this paper, four tillage treatments including conventional tillage with rice only system (CT), conventional tillage with rotation of rice and rape system (CTR), no-till and plain culture with rotation of rice and rape system (NTP) and no-till and ridge culture with rotation of rice and rape system (NTR) were selected as research objectives. The results showed that the annual CH4 and N2O emissions were mainly occurred in the rice growing period, and were about 77.6% and 55.0% of the total annual of them emitted from this period. The total annual CH4 under CT was higher than that of other treatments. The annual average flux of CH4[CH4, mg x (m2 x h)(-1)] order was CT (2.96 +/- 0.04)NTR (1.83 +/- 0.21)NTP (1.42 +/- 0.01)CTR (0.96 +/- 0.09); the annual average flux of N2O[N2O, microg x (m2 x h)(-1)] order was CTR (123.6 +/- 47.1)NTR (115.2 +/- 22.1)NTP (100.5 +/- 25.8)CT (81.3 +/- 13.5), and the total annual N2O under CTR was higher than that of CT. The global warming potentials (GWPs) of CH4 and N2O emissions under different tillage-cropping systems were assessed in an integrated way. The results showed that the integrated GWPs of CH4 and N2O emission were in the following sequence: CTNTRNTPCTR, and CTR was the best treatment for decrease the integrated GWPs in this area.